Tungsten-halogen cycle electric incandescent lamp and method of manufacturing

ABSTRACT

A tungsten-halogen cycle electric incandescent lamp has a fill including phosphorus and iodine, at least part of the iodine content having been formed by thermal dissociation of P2I4 within the lamp envelope. The P2I4 may be introduced in solution in a volatile non-polar organic liquid which is thereafter removed to leave the solid iodide. The fill may include iodine derived from dissociation within the lamp envelope of a further iodine compound or elementary iodine, and may additionally include a halogen other than iodine.

A United States Patent 1191 Coaton et al.

[ Nov. 11, 1975 1 TUNGSTEN-HALOGEN CYCLE ELECTRIC INCANDESCENT LAMP AND METHOD OF MANUFACTURING [75] Inventors: James Richard Coaton: John Michael Rees. both of London. England [73] Assignee: Thorn Electrical Industries Limited,

' London. England [22] Filed: Oct. 16, 1973 [21] Appl. No.: 406,946

[30] Foreign Application Priority Data Oct. 18. 1972 United Kingdom 48064/72 [52] US. Cl. 313/222; 313/223; 316/20 [51] Int. C13... HOIK 1/50; HOlJ 9/38; HOlJ 9/395 [58] Field of Search 316/17. 18. 19. 20. 21.

,[56] References Cited UNITED STATES PATENTS 3.475.649 10/1969 Nameda et a1 313/223 3.712.701 1/1973 Johnston et a1 316/20 3.810.685 5/1974 Coxon 316/20 FOREIGN PATENTS OR APPLICATIONS 271.777 11/1963 Australia 313/223 952.937 3/1964 United Kingdom 313/223 3/1966 United Kingdom 313/222 Primary E.\'lII11l I1LlR0 Lake Assistant E.\'uminer.lames W. Davie Atmrney. Age 11. Fl'rmRob en F OConnell [57] ABSTRACT 8 Claims. 1 Drawing Figure US. Patent Nov. 11, 1975 ii U TUNGSTENLHALOGEN CYCVLE ELECTRIC INCANDESCENT LAMP ANDVMETHOD or MANUFACTURING The present invention relates to tungsten-halogen cycle electric incandescent lamps. x l

These lamps employa tungsten filament in a transparent envelope, usually of fused silica, andafill of a non-reactive gas such as-N fA'r, Kr or Xetogether with a small quan tity of halogen Bromine, chlorine, fluorine and their compounds have 'beenproposed as the halogen. transport gas but owing to their re'activity are only suitablexfor high efficacy lamps ofshort life. Forlamps withan intendedlife. of l000hours or above iodine is necessary, or an iodine compound or a mixture with other halogens with iodine predominating.

There are serious difficulties attendant upon the introduction of elementary iodine into the lamp. Iodine has a vapour pressure which is too high for the lamp to be pumped after introduction of the element, but too low for the iodine to be flushed in at room temperature with the fill gas, such as argon. Cumbersome and expensive techniques are employed to overcome this difficulty, but often involve an undesirable number of manual operations, the risk of introducing harmful impurities or an inability to achieve an accurately controlled dosage of iodine.

In accordance with this invention these disadvantages are reduced with a tungsten-halogen cycle electric incandescent lamp having a fill including phosphorus and iodine, at least a part of the iodine content having been formed by thermal dissociation of P 1. within the lamp. Diphosphorus tetraiodide, P l is a low va pour pressure solid at room temperature. it is preferably introduced into the lamp in solution in a volatile, non-polar organic liquid, such as benzene or toluene.

This iodine compound in solution can be accurately dispensed into the envelope and the solvent can be removed by evacuation or by flushing with a dry nonreactive gas. After this the lamp can be evacuated on an exhaust system, which can be a rotary machine commonly used in the manufacture of incandescent lamps, and filled with non-reactive gas to the required pressure. The iodine compound is only dissociated when the lamp is heated, which is usually achieved by lighting the filament. The preferred procedure is to increase the filament voltage shown from zero to full voltage over about to 30 seconds to allow the compound to disperse, or to step age" the filament by running at various intermediate voltages, from zero to the rated voltage.

A source of iodine or other halogen may be introduced into the lamp envelope in addition to the P 1 The further halogen may be introduced in elementary form or in the form of a halogen compound.

By use of the invention a controlled and accurately repeatable quantity of iodine and phosphorus can be dispensed into each lamp. The phosphorus acts as a getter and during its manufacture the lamp of the invention is susceptible of close control of the ratio of halogen to phosphorus which we have found is desirable for optimum gettering action without adversely affecting the tungsten-halogen transport cycle. After the solvent has been removed, the remaining solid is involatile at room temperature and the lamp can be exhausted and gasfilled on a simple vacuum, gasfilling system of the type used for non-halogen lamps, without the need for cold traps orother devices .forprotecting 'rotary pumps, valve plates and othericomponents of the system. Because all-the-iodine remains as an involatile solid during processing, no special maintenance or safety precautions are require'd-on'the exhaust and gasfilling system, and the method isvery suitable for high speed production techniques.

This compoundhas the advantage over other alternatives, .such as Cl-l lfcl-l l CHl and Hlinthat hydrogen may be excludediaiicl an accurate ratio of iodine: phosphorus is dispensedinto "thelamp. However, it can be introduced into a lamp containing any halogen or halogen compound and'is'avery pr'ecise method for introducing a .getter into tungstemhalogen lamps.

The following are examples of thepractice of this invention:

EXAMPLE I Diphosphorus tetraiodide is dissolved in toluene to a concentration of 3percent weight/volume (i.e. 3g P l in l00 ml of toluene). To maintain a satisfactory tungsten transport cycle and an adequate gettering action in a 240V 500W coiled coil linear tungsten-halogen lamp, having an efficacy of 20 lm/W and 2000 hr life, 0.25 ml of this solution is required. it is introduced by inserting the needle of a suitably calibrated syringe into the exhaust tube of a lamp envelope, and injecting the required quantity into the lamp envelope. The solvent is then removed by inserted a hollow needle connected to a dry nitrogen supply, and flushing gas into the lamp until the solvent is removed. Raising the bulb wall temperature to approximately C speeds up this operation. This leaves an accurate quantity of the solid in the envelope.

After this the lamp is processed as a conventional incandescent lamp on a suitable exhaust/gasfilling system with the bulb at room temperature. After being filled with gas, and tipped-off, the lamp is then lit to dissociate and disperse the iodine compound.

A mixture of iodides may also be used to change the iodinezphosphorus ratio and the following is an example of such a case:

EXAMPLE 2.

A solution is prepared consisting of 0.05g P l and 0.45g CHl in ml of benzene. To maintain a satisfactory tungsten transport cycle with an adequate gettering action in 12V 55/43 twin filament tungsten-halogen motor vehicle headlight lamps, 0.03ml of this solution is injected. The solvent is removed and the lamp subsequently processed as described in the Example l.

The accompanying drawing shows an example of a lamp prepared as example of a lamp prepared as described in Example l.

The lamp has a high melting point glass envelope 8 provided with an aperture (not visible) through which the envelope 8 was exhausted and filled. The lamp was thereafter sealed by sealing off an exhaust tube with which the aperture was provided. The envelope has two lead-in wires 12 sealed therethrough connected to the generally linear tungsten filament 9. The lead-in wires are connected to conductive end caps 13 at either end of and on the exterior of the envelope 8.

We claim:

1. A method of making a tungstenhalogen cycle electric incandescent lamp comprising the steps of:

providing a light-transmitting high-temperature resisting envelope having an aperture therein, a tungsten filament therewithin, and lead-in wires connected to said filament and sealed therethr'ough; introducing P l. into said envelope through said aperture; exhausting said envelope; gas filling said envelope with a non-reactive gas; sealing said aperture; and raising said envelope to a high temperature sufficient to dissociate said P 1 the introduction of said P l. being in a manner such as to produce said P l in solid form prior to the raising of said envelope to said high temperature.

2. A method claimed in claimedin claim 1 wherein P 1 is introduced into said envelope in solution in a volatile non-polar organic liquid which is thereafter removed to leave solid'P l 3. A method as claimed in claim 1 and further including the steps of introducing a source of iodine into said envelope in addition to said P l,,

4. A method as claimed in claim I and further includ' ing the steps of introducing a source of halogen other than iodine into said envelope in addition to said P 1 5. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim 1.

6. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim 2.

7. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim 3.

8. A tungsten-halogen cycle electric incandescent lamp made in accordance with'the method of claim 4. 

1. A METHOD OF MAKING A TUNGSTENHALOGEN CYCLE ELECTRIC INCANDESCENT LAMP COMPRISING THE STEP OF: PROVIDING A LIGHT-TRANSMITTING H HIGH-TEMPERATURE RESISTING ENVELOPE HAVING AN APERTURE THEREIN, A TUNGSTEN FILAMENT THEREWITHIN, SAID LEAD-IN WIRES CONNECTED TO SAID FILAMENT AND SEALED THERETHOUGH. INTRODUCING P2I3 INTO SAID ENVELOPE THROUGH SAID APERTURE; EXHAUSTING SAID ENVELOPE; GAS FILLING SAID ENVELOPE WITH A NON-REACTIVE GAS; SEALING SAID APERTURE; AND RAISING SAID ENVELOPE TO A HIGH TEMPERATURE SUFFICIENT TO DISSOCIATE SAID P2I4, THE INTRODUCTION OF SAID P2I4 BEING IN A MANNER SUCH AS TO PRODUCE SAID P2I4 IN SOLID FORM PRIOR TO THE RAISING OF SAID ENVELOPE TO SAID HIGH TEMPERATURE.
 2. A method claimed in claimedin claim 1 wherein P2I4 is introduced into said envelope in solution in a volatile non-polar organic liquid which is thereafter removed to leave solid P2I4.
 3. A method as claimed in claim 1 and further including the steps of introducing a source of iodine into said envelope in addition to said P2I4.
 4. A method as claimed in claim 1 and further including the steps of introducing a source of halogen other than iodine into said envelope in addition to said P214.
 5. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim
 1. 6. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim
 2. 7. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim
 3. 8. A tungsten-halogen cycle electric incandescent lamp made in accordance with the method of claim
 4. 